An operating or command element in the form of a push button which has a level key plate is known from prior art. The round key plate has a circumferential ring as a surface elevation on the edge of the key plate so that when the push button is arranged horizontally or lying down, a flat depression is formed on the key plate.
On a reverse side, the push button has a level contact surface, which is parallel to the front side of the key plate and in the installation position of the push button abuts against a front plate of a housing, control cabinet, or the like and, therefore, determines the position of the push button. Usually, a part of the push button reaches through an opening in the wall of the housing. The part located outside the housing, i.e., the key plate with the circumferential ring, can become more or less heavily soiled depending upon the area of application. If the push button is used in the field of hygiene it must, as a rule, be cleaned regularly with a liquid cleaning agent.
If, however, the push button is used in a horizontal installation position, the liquid cleaning agent accumulates in the depression and cannot flow off. This is unacceptable, and not just for hygiene reasons, thereby excluding the use of the push button for such installation positions.
Furthermore, a push button is known from the prior art whose key plate, which is also round, is completely level. With such a push button, no liquid cleaning agent accumulates during the cleaning of the push button. Disadvantageous, however, is the fact that detection of a completely level push button is practically impossible. Therefore, an operator cannot detect such a push button blindly (that is, by feeling with his fingertip), as would, however, be possible with the previously described push button with the circumferential ring.
DE 10 2006 055 249 shows an operating element with a key plate on which nubs are arranged for the purpose of improving the grip. DE 39 23 747 A1 discloses an actuator for electrical switchgears, wherein a push button is designed in the form of a quadratic plate on which the nubs projecting upwards represent individual characters in braille. DE 2 361 639 discloses a push button for outdoor facilities which is supposed to be less susceptible to blockages caused by ice. All of these operating elements, however, have in common that they cannot be put to use universally in the field of hygiene.